This is an application to investigate the organization of the neural network that mediates the learning and production of complex vocalizations by oscine songbirds, a unique model system for studying the brain mechanisms of motor skill learning. The general hypothesis to be tested is that the songbird vocal control system depends critically on non-auditory feedback information both for coordinated vocal production and for vocal learning. It is further postulated that an important component of this feedback is mediated by neuronal pathways that are entirely central ("internal" feedback) and that project to vocal control areas in the forebrain. One possible function for such pathways is to maintain synchronized output from the two sides of the forebrain during singing. To determine whether interhemispheric synchrony is continuously maintained, the neural activity of a forebrain song control nucleus will be monitored during singing while the activity in its contralateral homologue is forced out of synchrony using electrical stimulation. Additional experiments will test the hypothesis that a thalamic nucleus (Uva) which projects to forebrain song control nuclei is involved in maintaining interhemispheric synchrony during singing. This will be done by (1) assessing with bilateral neurophysiological recordings the capacity to maintain synchrony with and without nucleus Uva and (2) by searching for bilateral projections from midbrain or lower parts of the vocal control system to Uva. A second possible role for this thalamic pathway to forebrain song control nuclei is to convey proprioceptive feedback information during song learning. This possibility will be tested by determining the electrophysiological responses of Uva neurons to proprioceptive activation and by obtaining a developmental profile of these proprioceptive responses. To learn complex motor skills, feedback information about performance and body state are required. Auditory feedback is critical for song learning, but nothing is known about the roles or substrates of non-auditory feedback information in the learning and coordination of birdsong. The proposed studies will provide new insights on how neuronal feedback pathways contribute to the process of song learning in particular and to the learning of motor skills in general. This research will contribute to the understanding of how the brain acquires and retrieves complex motor skills.